Electrostatic atomizers for producing atomized liquids are known. Electrostatic atomizing devices for atomizing a liquid having low conductivity are disclosed in U.S. Pat. Nos. 4,255,777, 4,380,786, 4,581,675, 4,991,774, and 5,093,602 to Kelly, the disclosures of which are hereby incorporated by reference herein. The electrostatic atomizer of U.S. Pat. No. 4,255,777 is capable of forming droplets having an average diameter of less than about 1 millimeter for a liquid having a low conductivity. Using an electrostatic atomizer like that of U.S. Pat. No. 4,255,777, hydrocarbon fuels can be efficiently burned in a combustion device because the atomizer can produce droplets of fuel of such a small size. Fuels which are challenging to burn can be atomized with a sufficient flow rate for a compact combustion device utilizing such an atomizer.
A combustion device using an electrostatic atomizer is disclosed by U.S. Pat. No. 5,695,328 to DeFreitas et al., the disclosure of which is hereby incorporated by reference herein. This patent discloses an ignition device useful for engine combustors in which the electrostatic atomizer of U.S. Pat. No. 4,255,777 may be used. In this device, the voltage is varied to vary the fuel droplet size produced by the atomizer and to thereby vary the thermal output for the device.
In electrostatic atomization according to the aforementioned patents and patent applications, electrical charges from an electrode are injected into the fluid to be atomized, so that the fluid has a net (charge, typically a negative charge. Fuel droplets are formed in the above-discussed electrostatic atomizers under the influence of electrostatic forces within the fluid. The size of the fuel droplets produced is independent of the flow rate. Droplet sizes which are a fraction of the orifice diameter can be produced. Thus, details of the orifice cross-section, such as the geometry of the orifice and its alignment with the emitter, do not affect the atomizer's ability to produce a regularly shaped plume of self-dispersed fuel. In certain atomizers according to U.S. Pat. Nos. 5,093,602, 5,378,957, 5,391,958, and 5,478,266 of Kelly, the disclosures of which are also hereby incorporated by reference herein, a charge is injected onto the fluid using an electron beam. These designs provide similar atomization.
It would be desirable to provide an electrostatic atomizer and a combustion device incorporating an electrostatic atomizer having an orifice design which exploits the fact that the orifice design and flow rate are independent of the atomization of the liquid.